The present invention relates to a cantilever turbocharger in which a turbine and a compressor are disposed in back-to-back relationship and a bearing is disposed on the side of suction (on the side of the compressor).
In the conventional turbochargers, a bearing casing incorporating bearings is interposed between a turbine casing and a compressor casing so that heat from the turbine is not directly transmitted to the compressor but to the bearings so that some countermeasures must be taken so as to protect them.
In order to prevent the bearing from being overheated, there has been devised and demonstrated a cantilever type turbocharger in which the turbine and the compressor are disposed in back-to-back relationship and the bearing is disposed on the suction side. However, with the cantilever type turbocharger, heat from the turbine is transmitted to the compressor so that the temperature of the compressor is increased and consequently the efficiency is considerably decreased. The decrease in efficiency includes an apparent decrease in efficiency due to heating after the discharge of compressed air, but there still remains the problem that because of the increase in specific volume of intake air, the supercharging effect on the displacement (reciprocating) type engine is adversely affected. In addition, the turbocharger is of the cantilever type so that the load exerted on a support on the side of the compressor is very high. As a result, the temperature of the antifriction bearing such as ball bearing rises so that the service life thereof which is in general short becomes shorter.
In the cantilever type turbocharger of the type described, the antifriction bearing is directly supported by a bearing housing disposed within the bearing casing so that no damper mechanism for absorbing the vibration caused by the unbalance of the turbine shaft works and consequently durability of the antifriction bearing which is weak under vibration is adversely affected. Furthermore, in order to lubricate the antifriction bearing, the capillary action of a wick is utilized so that the quantity of lubricating oil supplied to the antifriction bearing is very small. Therefore, there arises the problem that the lubricating oil is not sufficiently supplied to the antifriction bearing and the turbine shaft which is rotating at a high speed so that the service life of the antifriction bearing is shortened. Furthermore there is the problem that since the antifriction bearing is of the shaft-groove type without proper inner race, it is difficult to machine the shaft.
In view of the above, in a turbocharger of the type in which a turbine and a compressor are disposed in back-to-back relationship and a bearing is disposed on the suction side, a first object of the present invention is to provide a turbocharger in which a water-cooled casing is interposed between a turbine casing and a compressor casing so that the effect of shielding thermally between the turbine and compressor is improved and consequently the supercharging efficiency and the service life of the bearing can be improved and in which a cooling device with the water-cooled casing simple in construction is provided.
A second object of the present invention is to provide a turbocharger in which the life of the antifriction bearing is increased and which is provided with a bearing device which can improve sealability of a lubricating oil and make it simple to machine a shaft.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of some preferred embodiments thereof taken in conjunction with the accompanying drawings.